Effects of Low Temperature Annealing on the Transport Properties of Zinc Tin Nitride

TL;DR

This study investigates how low-temperature annealing affects the electrical transport properties of ZnSnN2 thin films, revealing significant reductions in carrier density but also decreases in mobility, emphasizing the importance of optimized growth conditions.

Contribution

It provides a systematic analysis of annealing effects on ZnSnN2 films, highlighting the need for controlled growth to achieve photovoltaic-quality materials.

Findings

Annealing reduces carrier density by up to 80% in zinc-rich films.

Mobility decreases with increasing annealing time.

Initial film disorder limits the benefits of annealing.

Abstract

ZnSnN2 has recently garnered increasing interest as a potential solar absorber material due to its direct bandgap that is predicted to be tunable from 1.0-2.1 eV based on cation disorder. One important challenge to the further development of this material for photovoltaics (PV) is to reliably synthesize films with carrier density less than or equal to 10^17 electrons/cm^3. In this work, we perform a systematic annealing study on compositionally-graded Zn-Sn-N thin films to determine the effects on carrier density and transport of such post-growth treatment. We find that annealing up to 6 hr under an activated nitrogen atmosphere results in a reduction in carrier density by ~80% for zinc-rich films, and by ~50% for stoichiometric films. However, we also find that annealing reduces mobility as a function of increasing annealing time. This result suggests that initial film disorder hampers the benefits to film quality that should have been gained through annealing. This finding highlights that carefully managed initial growth conditions will be necessary to obtain PV-quality ZnSnN2 absorber films.